A battery is a device to convert chemical energy of chemicals into electrical energy through electrochemical reaction, and is classified into two categories: a primary battery and a secondary battery. Among the rechargeable secondary battery, a lithium secondary battery is the most important one, because it has the highest voltage and the largest energy density among existing batteries.
One of the conventional methods for fabricating the lithium secondary battery is described in FIG. 6. The lithium secondary battery according to the method is fabricated by successively depositing a grid-type anode current collector 11, a matrix-film type anode 12, a matrix-film type separator 13, a matrix-film type cathode 14 and a grid-type cathode current collector 15, followed by laminating the members to integrate them and folding the laminated members in a zig-zag fashion. More detailed explanation can be obtained by U.S. Pat. No. 5,460,904. The secondary lithium battery fabricated by the method (“integrated lithium secondary battery”) comprises both the anode and the cathode in an integral from, and it suffers from the disadvantage that damage to the electrodes sometimes occurs in the folding process.
In order to avoid the above disadvantages, KR 309,604 and 336,396 disclose examples in which a plurality of anode plates and a plurality of cathode plates are used. FIG. 7 is a cross sectional view showing an arrangement of a plurality of anode plates and cathode plates in a separator, in accordance with the KR 309,604. The methods disclosed in KR 309,604 and 336,396 comprises adhering a plurality of anode plates 22 to one surface of the separator 21 with a predetermined interval (a distance inside which at least one electrode plate can be inserted), adhering a plurality of cathode plates 23 to the other surface of the separator 21 with a predetermined interval (a gap inside which at least one electrode plate can be inserted), and folding the separator in a zig-zag fashion to obtain a lithium secondary battery having a stacked structure in which each of the anode plates 22 and each of the cathode plates 23 are alternatively stacked. Unexplained reference numeral 24 is an adhesive layer. The stacked lithium secondary battery avoids the disadvantage of the above mentioned integrated lithium secondary battery; this method can prevent the damage to the electrode caused by a folding process. However, they are also suffered from the disadvantages that the folding process is complicated, and that it is difficult to tightly fasten the separator because folding of the separator is performed in zig-zag fashion. The gap formed between the electrodes and the separator and caused by loose fastening of the separator deteriorates cycle life of an electrochemical cell and charge/discharge characteristics. Particularly, as the surface area of the electrode is larger, the probability of the gap formation is higher, which makes it difficult to fabricate a cell having uniform electrical property. Further, as the electrode plates are adhered in a manner such that an interval within which at least one cathode or anode is inserted, the length of the separator to which the electrode plates are adhered is longer, which requires a larger facility and a larger working space.
KR published patent No. 2002-93781 by our present inventor discloses a method for fabricating a lithium secondary battery, comprising arranging both of the anode plates and the cathode plates onto one surface of the separator in a predetermined order, and then folding the separator in a fixed one-direction rather than in a zig-zag fashion. The method avoids the disadvantages caused by the zig-zag folding. However, the method suffers from a possible electrical short by neighboring arrangement of the cathode plate and the anode plate. In addition, the method also suffers from a requirement of a larger facility and a larger working space caused by larger length of the separator to which the electrode plates are adhered.
For these reasons, new stacked lithium secondary battery and its fabrication which solves the disadvantages caused by the zig-zag folding (difficulty of the folding process and reduced cycle life of the battery) and which prevent the possible electrical short are being demanded.